Long term forecasts of water usage for electricity generation: South Africa 2030

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South Africa’s energy sector is currently in a state of flux as a result of social, economic and environmental pressures. The need for more energy while sustaining the society, economy and environment calls for efficient management of resources. Water being one of the basic yet constrained resources is a vital component in electricity generation. Electricity generation is dominated by coal, which accounts for approximately 90% of the electricity generated. South Africa is expected to have a water deficit of 234 gigalitres by 2025, (based on conservative estimates) as projected within national accounts published by Statistics, South Africa. This research aimed to (1) Forecast water usage patterns associated with coal based electricity generation, both in l/kWh and total water consumption (in megalitres), (2) Assess scenarios of water usage patterns based on cooling technology and power plant type, and (3) Propose projected water saving measures within distressed water management areas.
The methodology used was built on work done by the National Energy Technology Laboratory, USA. The guideline study estimates water usage based on water withdrawal and consumption factors. The mathematical technique used to forecast total water consumption and water consumption factors is based on a long-term moving average approach. This approach relies on historical data of water consumption factors and generation output. The method takes into consideration the percentage change in system thermal efficiency which is a variable that has an influence on the water consumption factor of a power plant. Historical data of South African power plants was supplied by Eskom from archival records.
The investigation derived six key findings: (1) Water consumption factor forecasts of dry cooled power plants (ranging from 0.1 l/kWh to 0.15 l/kWh) are expected to be one order of a magnitude lower than wet cooled power plants (ranging from 2.2 l/kWh to 2.4 l/kWh). (2) Water consumption factor for the return to service (RTS) fleet (used during peak demand) is expected to reach 3 l/kWh by the year 2020. (3) Water requirements are expected to increase from roughly 360 gigalitres now to just above 370 gigalitres in 2021. (4) Depending on the retirement of the RTS fleet, total water requirements could be reduced (by 12% to 15%) to 320 gigalitres. (5) RTS power plants are located within water constrained water management areas Olifants and Inkomati. (6) Based on the projection the total base load water consumption will increase from 332 gigalitres in 2013 to roughly 370.5 gigalitres during 2035. These six findings are based on a forecast electricity output from the coal power plant fleet of 260 TWh by the year 2035, and on an expected installed capacity of 36900 MW being operated at 80% capacity.
Gradual retirement of the RTS fleet could result in a savings of 15% of the forecast shortfall of 234 gigalitres by the year 2025. The deficit in electricity generation output caused by the retirement of the RTS fleet will have to be compensated by the simultaneous commissioning and operation of new build power plants.